The present invention generally relates to a control system for a scanning arrangement and more particularly, to a control system for a scanning arrangement subjected to reciprocating movements by an electric motor controlled for its energization by a microcomputer. The scanning arrangement as referred to above is employed for an electrophotographic copying machine of a scanning exposure type, an image reader of a scanning type or the like.
Subsequently, the control system of the above described type will be explained hereinbelow with reference to a scanning arrangement of an electrophotographic copying machine.
Generally, electrophotographic copying machines are provided with different scanning modes, i.e. various scanning speeds and scanning distances according to sizes of original documents and copy paper sheets or copying magnifications. Therefore, scanning arrangements are required to be so controlled as to successfully carry out the intended scanning based on such scanning modes.
The reciprocating movements of a scanning arrangement include a displacement for scanning images of an original document (referred to as a scanning movement hereinbelow) and another displacement for returning to a home position which is a starting point of the scanning movement (referred to as a returning movement hereinbelow), and the control for the scanning movement is effected, for example, in such a manner that a driving motor is turned on and off in a predetermined very short period of time, while the time for the on period is increased or decreased according to the measured speed.
Meanwhile, for the control of the returning movement, there have been known the following two practices.
One practice is disclosed, for example, in U.S. Pat. No. 4,332,461 to Cail et al., in which a constant speed control is effected also in the returning period in the similar manner as in the scanning period, and in that case, the speed is raised to be high fcr acceleration of the returning of the scanning arrangement.
The other practice is such that all the restoring force is applied during the start of the return so as to apply braking at a predetermined timing, and in U.S. Pat. No. 4,371,254 to Beery, for example, it is so arranged that the scanning arrangement is caused to return by a restoring force of a return spring, with a magnet brake being applied at a predetermined timing during the returning.
For the improvements of the known practices as described above, there have been proposed by the present assignee, the control systems wherein the returning by the return spring is replaced by a returning utilizing a driving force of a motor, for example, in U.S. patent application No. 511,390 "A system for controlling the reciprocation of a scanning arrangement" by Ikenoue, filed July 5, 1983 and U.S. patent application No. 521,624 "A system for controlling reciprocation of a scanning arrangement" by Sugiura, filed Aug. 9, 1983.
In any of the above practices, the speed during the returning is adapted to be considerably high. If the power supply should be turned off by a certain cause while the scanning arrangement is returning at high speeds, said scanning arrangement is further displaced by the inertia, thus resulting in a violent collision thereof with a stopper member or the like provided at the home position in some cases.